“In addition, some fuel energy is required to light off the catalyst, and it takes time for the O2 (oxygen) sensor and the control system to be able to operate in closed-loop fuel control mode,” Anderson says.

Warmer ambient conditions such as a heated garage in winter will help a little because the starting temperatures of the oil and engine metal surfaces is slightly higher.

“It simply takes less time to heat up six quarts of oil from 25 degrees Celsius to 100 degrees Celsius than it does from zero C to 100 C,” says Anderson.

Many drivers use or are tempted by remote start devices that will allow the car to warm oil, clear windows and provide a comfy interior temperature. The U.S. Environmental Protection Agency suggests that whether via remote or actually climbing in and starting the engine yourself, letting a car idle to warm up hurts fuel economy.

“The EPA is correct,” Anderson says. “The vehicle's fuel economy while idling is 0 mpg. It is better to accumulate miles while warming up the vehicle to get some positive fuel economy.”

Another victim of idling is air quality. “Emissions such as hydrocarbons, carbon monoxide, nitrous oxides and carbon dioxide are typically measured in grams per mile, so it is better to be accumulating miles, that is, doing useful work, while generating any level of emissions, rather than idling at a standstill.” Anderson says.

When the vehicle is driven cold, the more heavily loaded engine accelerates the warmup process and gets the engine to operate with lower emissions more quickly.

An unheated garage attached to a heated home is generally warmer than the cold ambient temperatures in the winter, says Anderson. So the starting temperatures of the oil and engine metal surfaces would still be higher than if the vehicle were parked outside, and there would be a little acceleration of the warmup process.

“The temperature in a freestanding non-heated garage would be very close to ambient temperature, so there would likely be very little acceleration of the warmup period,” he says.

The purpose of remote start is to help warm up the vehicle as a convenience, especially on cold days, he says.

Just so things don’t get out of hand with respect to emissions and fuel consumption, Anderson notes that that GM’s remote start systems shut down the engine after 10 minutes of idling.